Manufacturers of consumer electronics devices, such as laptops, tablets, and smart phones, are demanding 3D glass covers for their displays. These 3D glass covers would have printed designs on their inside surfaces. When the devices are assembled with the 3D glass covers, the printed designs would hide the innards of the devices while providing clear apertures for the displays to operate. The printed designs would be required to meet very precise specifications. For small display applications, such as smart phones, meeting these very precise specifications economically is challenging.
Screen printing is a method that is widely used for printing designs on surfaces. In screen printing, a design is created on a fine mesh material called a screen. The design is created by masking off certain areas of the screen while leaving other areas open. The screen with the design is stretched on a frame. Then, a paste of ink is applied on the screen using a floodbar. A machine or operator draws a squeegee across the screen while applying a load to the squeegee. As the squeegee is drawn across the screen, ink is pushed through the open areas of the screen onto the surface.
U.S. Pat. No. 6,698,345 issued to Cutcher (the '345 patent) describes a method and an apparatus for screen printing on the inside surface of a curved substrate. The method includes mounting the curved substrate in a recess of a support member. The curved substrate is urged against the recess by vacuum. The inside surface of the curved substrate is brought into contact with a screen mounted on a screen mounting frame that is capable of conforming to the inside surface. The screen mounting frame has a right side, a left side, a front portion, and a rear portion. The right and left sides each have vertically movable center portions and end portions, where the center portions are each bounded by at least two hinges. The screen mounting frame is deflected by means of these movable and hinged portions.
In the method of the '345 patent, ink is applied to the screen while the screen is in a generally flat, horizontal position. The screen mounting frame is deflected, as described above, to substantially conform the screen to the inside surface of the curved substrate. Then, the ink is urged through the deflected screen with a squeegee. The squeegee is attached to a pendulum capable of pivotal movement. The length of the pendulum arm may be fixed or adjustable. The '345 patent discloses that the method may be employed to print a pattern on the inside surface of a curved substrate where the radius of curvature is approximately 20-80 inches, measured from the pivotal mounting point of the pendulum.